Altered calpastatin protein levels following traumatic brain injury in rat

Pathological activation of the intracellular Ca2+-dependent proteases calpa ins may be responsible for the neuronal pathology associated with neurodege nerative diseases and acute traumas to the central nervous system. Though c alpain activation has been shown definitively in traumatic brain injury (TB I), no studies have investigated calpastatin (CAST), the calpains' endogeno us and specific inhibitor, after TBI, The present study examined temporal c hanges in CAST protein following controlled cortical impact injury in the r at. Western blot analyses of CAST in cortex and hippocampus detected two ba nds corresponding to molecular weights of 130 kDa [high-molecular-weight (H MW)] and 80 kDa [low-molecular-weight (LMW)]. A modest decrease in the HMW band in conjunction with a significant increase in the LMW band was observe d in cortex ipsilateral to the site of impact following TBI, Examination of ipsilateral hippocampus revealed an increasing trend in the LMW band after injury, while no changes were observed in the HMW band, Thus, observable c hanges in CAST levels appear to occur several hours after reported calpain activation and cleavage of other substrates, In addition, a new analysis wa s performed on previously published data examining calpain activity in the same tissue samples used in the present study. These data suggest an associ ation between decreases in calpain activity and accumulation of LMW CAST in the ipsilateral cortex following TBI, The present study cannot exclude pro teolytic processing of CAST to LMW forms, However, the absence of reciproci ty between changes in LMW and HMW bands in consistent with other data sugge sting that rat brain could contain different CAST isoforms.